


Fathoms Below

by InsomiCat, Lost_and_Found (Da_Boss_Is_Here)



Category: The Little Mermaid - All Media Types, 僕のヒーローアカデミア | Boku no Hero Academia | My Hero Academia
Genre: 2am Ideas, All for one is Ursula, Little Mermaid AU, Present mic is scuttle, We should be sleeping, aizawa is Sebastian, all might is triton, bakugou is prince eric, but writers never rest!, izuku is flounder, kirishima is Ariel
Language: English
Status: Completed
Published: 2020-04-25
Updated: 2020-04-25
Packaged: 2021-03-01 22:41:10
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,986
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23834767
Author URL: https://archiveofourown.org/users/InsomiCat/pseuds/InsomiCat, https://archiveofourown.org/users/Da_Boss_Is_Here/pseuds/Lost_and_Found
Summary: Little mermaid au with bnha characters
Relationships: Bakugou Katsuki/Kirishima Eijirou
Kudos: 12





	Fathoms Below

Kirishima, Izuku, and Aizawa explore a shipwreck while Kirishima’s family performs in a concert which he is supposed to be in. After having the loot he got from the shipwreck inspected by mic, who “knows” all about human things, he deposits his loot in his Human Treasure Cave. 

He gets yelled at once he’s home by his father, All Might, who tells him to stay away from humans. Kirishima talks to his siblings for a bit, telling them how wonderful the human world is, but they think he’s a bit weird for liking it. 

Later, Kirishima sneaks out to look at a ship, where men are dancing and singing and having a blast. A handsome man plays a flute while he and his dog dance. 

Kirishima is entranced. Kirishima learns his name- Prince Bakugou- when the man is addressed as he receives a statue of himself as a gift, which he clearly hates but is reluctantly polite about it. 

The ship hits a storm and starts to sink, as it was struck by lightning and is now on fire. Bakugou goes back on board once everyone’s out to get his dog, but he falls into the water before he can get to safety. Kirishima is unwilling to let someone be killed without trying to help them, and struggles to bring Bakugou to shore. Laying the man on the sand, Kirishima tries to wake him. 

Bakugo awakes to a silhouetted Kirishima, who’s gently singing to him. Once he wakes up, Kirishima panics and leaves. On his way home, he grabs the statue to put in the Cave. Aizawa, who feared for Kirishima's life, had alerted All Might- unbeknownst to Kirishima.

He returns to the Cave, as All Might is swiftly making his way there to knock out the nonsense of Kirishima’s human infatuation. 

Kirishima carefully places the statue in the cave, stroking the smooth stone cheek longingly when All Might bursts in. He yells at his son, angry that Kirishima had disobeyed his orders to leave the human world alone. His eyes fall on the statue as Kirishima ducks behind it, and scowls fiercely. “I shall destroy this nonsense and you will go home!”

Kirishima protested tearfully, “But Dad! I love him!” But it’s to no avail. All Might destroys everything in the cave. 

Kirishima is heartbroken, and wants only to join the people on land. He flees his father, swimming aimlessly. Before long, he is discovered by the Sea warlock, All for One, who wants to “help” him. 

Kirishima follows him to his lair, where Kirishima encounters Shinso, All for One’s apprentice. Shinso is startled, and Kiri waves at him before the purple haired mer ducks out of sight. 

All for One tells Kirishima of the contract he could make; Kirishima could walk on land for 3 days, and if the prince kisses him, he’ll remain there. All it would cost was his voice, and if the prince didn’t kiss him, his soul belonged to all for one. 

Shinso peaks out from behind a rock ledge, shaking his head frantically, not verbally going against All for One but trying to tell Kirishima how bad of an idea this is. 

Kirishima signs the contract, and not long after loses his ability to speak. He swims up to the surface, knowing he won’t be able to breath soon, and is seen by Izuku and Aizawa. 

They chase after him, and watch in disbelief as his tail disappears, transforming into two legs. They follow him, waiting to see if he’ll survive getting washed ashore. 

Kirishima wakes up on the warm sand, and is amazed, the air has a taste he’s never noticed before. Salt and sun and something...indescribable. The wind whisks through his hair, blowing it into his eyes. His hair looks different and he tugs a lock into view. His hair is no longer red? He frowns in confusion at the chunk of black hair in front of his eyes before deciding to ignore it for now. 

He sits up awkwardly, gaze falling to his tail. No, he has legs now! He wiggles the small nubs on the ends. Legs! Feet! And toes! He has toes! He’s overjoyed to be human, finally. 

His friends call out to him, Aizawa immediately deduces that Kirishima met with the Sea Warlock, as All Might is the only other person who could transform him and All Might would never.

Mic, who thought the merman he’d talked to was simply washed ashore, is shocked to see him with legs. Mic gets him some cloth to wear, but is soon scared off by a familiar looking dog, who barks at Kirishima in recognition. 

Soon after, Bakugou chases the dog onto the beach. He looks up to meet Kirishima’s eyes. Kirishima looks familiar, but he doesn’t know how or why. 

When Bakugou asks for Kirishima’s name, Kiri can’t reply, instead grinning and pointing at his throat. Bakugou, realizing he can’t speak, takes him to his castle to get him dressed properly and to feed the stranger. 

As he is dressed in clothes- the color reminding him of foamy waves dappled in sunlight- Kirishima nods along with the conversation, learning more about where he is and who Bakugou is as a person and a prince. Kiri goes on a carriage ride with the prince, who’s enamored with Kirishima’s bewilderment and wonder towards the world. They take a boat ride and Bakugou is trying to guess Kirishima’s name but keeps getting it completely wrong. Aizawa sighs in frustration. He hauls himself up on a reed and says “His name is Kirishima.” Before jumping back in the water. Bakugou leans in for a kiss but the boat rocks wildly before tipping over. The two go back to the castle to rest for the night. 

Kirishima wakes up the next day, excited to see the prince again. Kirishima is met by Iida, who asks if he’s excited for the wedding. Kirishima, confused, listens as Iida tells him about Prince Bakugou’s arranged marriage to Prince Hitoshi from a neighboring kingdom. Heartbroken once again, Kirishima runs back to his room, sobbing. 

We cut to the rehearsal for the wedding, where Bakugou and Hitoshi are going through the plans for the ceremony on a large ship. Bakugou sounds out of it, like he’s not even there. The priest calls for a break, and Hitoshi heads to a room on the ship. Kirishima, curious, follows Hitoshi. Once he’s alone, Hitoshi, now revealed to be Shinsou, calls All for one to report on the progress of the plan. He cries after the call. Shinsou wants nothing more than to drop this plot of All for one’s, but he can’t risk Eri’s safety for something so trivial. He ends the call, leaning against a wall and starts to cry. Kirishima approaches, confused. Shinsou spots Kirishima and breaks down. He grabs the necklace anchoring the spells and crushes it-shattering the spells and releasing Kirishima’s voice. He confesses everything- All for One holding his sister as a hostage, the plan to prevent the kiss- everything. 

Kirishima is furious at All for One; Shinsou is being ordered to do terrible things, and he’s far more trapped than Kirishima ever felt in the castle. Kirishima empathizes with him, and decides to hatch a plan to foil All for One and free his newfound ally.

At the wedding, with Bakugou glass-eyed and Shinsou indifferent, the priest asks for the couple’s vows. The priest asks for any objections, to which Kirishima speaks for the first time in front of Bakugou and the castle staff. They are shocked. Kirishima storms up the aisle, and Shinsou turns to look at him. Kirishima nods at Shinsou and is given a nod in return. He drops the spell he placed on the prince in order to have the marriage happen. 

All for One is watching from a short distance, hidden from sight. He is infuriated by Shinsou’s obvious rebellion and makes his appearance.  
At the same time All Might surfaces, having finally tracked down Kirishima. All for One starts berating Shinsou for ruining the plan. All for one, once he realizes that All Might is there, attacks All Might and takes the trident from him. 

Now powerful enough to destroy all that has wronged him, all for one starts by sending a bolt of magic at All Might, transforming him into a withered creature that resembles a (unholy) cross between a worm and a piece of kelp. Then he turns to destroying the boat full of traitors and witnesses. Kirishima and Shinsou leap off the boat as it begins to sink, tugging Bakugou with them. 

Shinsou waits anxiously for his tail to come back, the transformation finally happening right before they hit the water. He swims through the churning waters, leaving Bakugou on a rock where the man won’t risk being dragged under.

With Shinsou by his side, Kirishima hauls himself up onto one of the boats still afloat. It’s a wreck, waves buffeting it around but he grits his teeth, eyes narrow with determination. He steers the ship towards All for One’s back, the warlock distracted by destroying the remaining boats and with a crash of thunder, the splintered bow impales him. Kirishima is flung off the side of the ship by the impact and hits the water.

He sinks down through the slowly calming sea, and Shinsou catches him, pulling Kirishima back up to the surface near Bakugou. They both watch him with worry. Light swirls around Kirishima’s body, blindingly bright. As it fades away, it reveals Kirishima, bright red hair and tail replacing his previous legs and black hair. 

Kirishima swims to where they left Bakugou, with his clothes tattered and skin bruised. He was alive though. That’s all Kirishima could hope for. Kirishima explains what happened -his lifelong love of humans, the cave, the deal, everything that mattered- and apologizes for dragging Bakugou into this. Bakugou calls him an idiot: Kirishima isn’t responsible for All for One’s actions. Bakugou is just glad they both made it out alive after that. 

Kirishima realizes that, since he’s no longer human, he can’t stay with Bakugou anymore. He looks for Shinsou and begs him to help, but Shinsou can’t transform people. Only the warlock could. All might, back to his true form, corrects Shinsou: he can transform merfolk into humans as well. 

Kirishima pleads with him, hoping that his father has changed. All Might apologizes, seeing the error in his ways too late to help originally. He can, however, help now. 

All Might, trident in hand once more, turns his son into a human. They hug, finally understanding each other. Kirishima swims to Bakugou, and swims him to the shore, closer than anyone thought during the battle. Bakugou sits up, really seeing Kirishima for the first time since the fight. Kirishima stands tall, a loose aqua tunic edged with golden embroidery draped over his torso and loose pants to match.

He stands in front of the water as if ready to leave at any second. Bakugou calls out, hoping he won’t. Kirishima runs to him, and they embrace, together after all that’s happened. All Might looks on with a bittersweet smile on his face. His son has never been so happy.

Shinsou, after seeing Kirishima reconcile with his dad, swims down to All for One’s lair. The lost souls once trapped are now merfolk swimming out and away from the wretched cave that was their prison. Shinsou searches for a trap door, or a hidden room, knowing his sister is imprisoned somewhere within the walls. He soon finds what he needs: a door that was hidden behind a shelf, with a small food slot in the door. He calls for Eri. She replies softly, and he pushes the shelf over to reach the door handle. Within seconds it’s open, and Shinsou holds Eri close. They both begin to cry, relieved to be reunited.


End file.
